Evaluating Agro-Based Waste Materials for Cyanotoxin Sorption for Future Incorporation in Nature-Based Solution Units (NBSUs)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript is a comprehensive and well-written report evaluating unmodified agro-based waste materials (rice husks, olive pulp pomace pellets, cork granules) and the benchmark NBSU substrates (biochar, light expanded clay aggregates (LECA), and sand) for their microcystin-LR (MC-LR) and cylindrospermopsin (CYN) sorption potential. To my opinion, the manuscript does add valuable new information in the field. There are only few minor points, which could be improved to increase the manuscript’s reader-friendliness and correct some minor mistakes, as indicated below:

 

Points for Revision:

 

Affiliations:

- No. 4 institution does not correspond to any author.

 

2. Materials and Methods:

- Page 4, line 141: Would be good to indicate the rice species that the husk was obtained from, in order to allow for better replication of the experiments.

- Page 4, line 142: Please indicate the material that the biochar was obtained from.

- Page 4, lines 159-160 (and many other instances in the text): Please provide all scientific species names in italics throughout the manuscript.

- Page 5, lines 197-198: Why is 100μg/L considered a relevant environmental concentration? One could argue that, for instance, 1mg/L could be an even more relevant concentration, taking into account the WHO guidelines.

- Page 6, lines 252-253: The correct reference is Zervou et al.

- Page 6, line 254: Please specify the system manufacturer (most probably Waters Corporation?).

4. Discussion:

- Page 14, line 444: Was the sorption capacity of OP in the case of CYN reported indeed? It appears that this statement needs some rephrasing.

- Page 15, lines 490-491: “In a practical setting there would be other pollutants present in the water to be treated which would influence the sorption of cyanotoxins”: Please discuss this statement further and provide some references.

- Page 15, lines 493-494: “This includes vegetation, oxygen transfer, pollutant loading, flow direction, area, temperature, etc.”: Please provide some references on this.

- Page 17, lines 572-573: “NBSUs also have other components contributing to the degradation or removal of cyanotoxins”. Please provide some examples of other components.

Supplementary material:

- Table S2: Please explain why in certain cases (e.g. cork), the removal percentages drop

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

I have had the opportunity to review your article entitled “Evaluating Agro-based Waste Materials for Cyanotoxin Sorption for Future Incorporation in Nature-based Solution Units (NBSUs).” I find the topic particularly relevant for Water and believe it may attract significant attention from its readership. While the manuscript is well-written in most sections, I have provided comments below to assist in improving the quality and presentation of your work.

Comments:

Introduction:  

The introduction is well-structured, provides sufficient background, and clearly outlines the hypothesis and objectives. However, I recommend revising lines 133–134 to avoid a two-line paragraph. Consider linking this excerpt with the previous paragraph (lines 126–132) or expanding the last paragraph to avoid ending with a very short paragraph.

Methodology:  

Please revise the methodology section. I noticed a typographical error with the degree symbol starting on line 165.  

Ensure that microorganism genus and species names are italicized throughout the text.  

Line 234: The equation currently placed in Table 1 at the end of the methodology section should be moved. I recommend providing the equation immediately after it is cited in the text using the equation function and the appropriate reference. Additionally, ensure that all details and explanations of the equations are provided in the main text (relocate information from Section 2.6 as needed).  

Results:  

Perform a thorough copy-edit of the manuscript. For example, correct the typographical error “were>” on line 341.  

Figures: Improve the presentation of all figures. For Figure 1, start by removing the gridlines and revising the X and Y axes. Correct the typo “removal%” in Figure 1 and ensure a standardized format for all axis labels.  

Lines 366–367: Avoid a two-line paragraph.  

Section 3.2:  

Improve the presentation of Figure 2 by removing gridlines and arranging the panels horizontally instead of vertically.  

Enhance Figure 3 as well. For example, check the X-axis title in Figure 3b (“ɛ2 J2mol-2”) and correct it.  

SEM/EDS Results:  

This section requires better presentation. Clarify the goals and explain what type of information is intended to be obtained using 100X magnification. At this magnification, what significant pore dimensions (micro, meso, macro) can be observed?  

Clearly state the goals and analysis parameters in the methodology section. Provide a summary of these in the results section.  

I suggest presenting EDS results as bar graphs (quantitative results) or including numerical values for key elements in the text, while keeping the EDS spectra in the supplementary materials. The current presentation makes it difficult to interpret quantitative data.

Discussion:  

Lines 451–454: Direct the discussion toward a physicochemical analysis. What is the theoretical average size of the molecules targeted for adsorption? What are the theoretical pore sizes of the employed biomass? Which chemical groups favor adsorption of these molecules? Discuss these points thoroughly, as previous studies suggest that agri-food byproducts (e.g., rice husk) are effective adsorbents for various compounds.  

Replace "R2" with "R²" throughout the discussion.  

Provide a more detailed discussion of the results in Table 2 (line 389), particularly comparing qe, k1 and k2 for biochar and LECA adsorbents.  

Sections 4.2 and 4.3:  

Clearly state the advantages and disadvantages of using biochar and LECA in real-world scenarios where cost-effectiveness is a critical factor. Include an estimate of the costs of the employed biochar and LECA, and discuss how these costs compare based on the contaminant adsorption index per dollar.  

Despite the extensive discussion, there is a lack of clarity on how your results contribute to the existing state of the art. Explicitly state how your findings address gaps in knowledge regarding the use of biochar and LECA for cyanotoxin removal. Provide key references to support these contributions.  

Lines 580–581: Explain how 100X magnification provides sufficient information regarding the heterogeneous surface of the material. Does this refer to pore composition or another characteristic? Discuss how macroscopic heterogeneity is relevant, given that the key pores influencing adsorption are much smaller.  

Lines 583–589: Justify how EDS data from a few localized zones can be used to generalize conclusions about material heterogeneity. Provide references to support this assertion.  

Figure 2 (lines 10–20): Explain the slight reduction observed between these points for biochar. This requires a well-structured and convincing discussion to address more critical readers, considering the complexity of factors involved.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Dear authors, I have reviewed your revised manuscript and am satisfied with the improvements and corrections made